1. Technical Field
The present invention relates to an image forming apparatus.
2. Related Art
In an image forming apparatus such as a printer and a composite machine, a color image forming apparatus of a tandem type including multiple image forming units which respectively correspond to their associated color components has been developed.
Since this type of color image forming apparatus forms a color image while the toner images of the respective colors are superimposed on top of each other, in order to maintain the quality of the color image, the color image forming apparatus has a density correction control (a so called process control) function for correcting the toner densities of the respective colors and a color shift correction control (a so called resist control) function for correcting the shifted colors of the toner images of the respective colors.
Specifically, the density correction control function carries out the following control: that is, on an image carrier, there are formed the density correcting patches of the respective colors at given intervals; the densities of the respective patches are detected using a density sensor; and, when any lowered density is detected by the density sensor, there is executed a processing for maintaining the density of the image within a specified ranger for example, by supplying the toner of the color the toner density of which has been detected lowered.
Also, the color shift correction control function carries out the following control: that is, on an image carrier, there are formed color shift correcting patches for the respective colors at given intervals; the distances between the positions of the respective color shift correcting patches are measured according to the binary signal of the detect output from a density sensor; and, according to the measurement results, there is executed a color shift correcting processing.